Heretofore processes have been described for the thermal reaction between polybutenes (predominantly polyisobutenes) and maleic anhydride or like reactants whereby polybutenyl succinic anhydrides are formed. Some of the work along these lines is described, or at least referred to, for example in U.S. Pat. Nos. 3,018,247; 3,018,250; 3,018,291; 3,172,892; 3,184,474; 3,185,704; 3,194,812; 3,194,814; 3,202,678; 3,216,936; 3,219,666; 3,272,746; 3,287,271; 3,311,558; and in British Pat. No. 1 492 337. However as pointed out in U.S. Pat. Nos. 3,215,707 and 3,231,587, from the standpoint of commercial usefulness the alkylation of maleic anhydride with an olefinic hydrocarbon is very time-consuming and limited in its applicability to relatively low molecular weight olefinic hydrocarbon reactants, i.e., those having less than about 12-15 carbon atoms. These two patents further state that the higher molecular weight olefinic hydrocarbons are apparently not sufficiently reactive with maleic anhydride to be useful as an alkylating agent, and that higher molecular weight hydrocarbon-substituted succinic acid compounds are almost invariably prepared by reacting maleic anhydride with a halogenated high molecular weight hydrocarbon reactant. Indeed, in U.S. Pat. No. 4,234,435 it is reported that the process as described in these two patents is presently deemed best for preparing the substituted succinic acylating agents.
British Pat. No. 1 492 337 points out that while such acylating agents can be prepared by thermally reacting a polymer having an average molecular weight above about 200 with maleic anhydride at a temperature above 200.degree. C., the reaction rate of such reactions is low and that attempts to improve the reaction rate by increasing the temperature and/or by using superatmospheric pressure results in degradation of maleic anhydride to useless carbon dioxide, water and tarry solids.
U.S. Pat. No. 3,476,774 reports in Example 1 that reaction under nitrogen between polybutene and maleic anhydride conducted in a pressure vessel at 234.degree. C.-236.degree. C. for 6 hours and 40 minutes in o-dichlorobenzene solvent gave an alkenyl succinic anhydride product that had particles of sludge suspended in it. Improvements in yield are reported in Examples 2-4 of the patent wherein a thermal stabilizer (4,4'-methylenebis(2,6-di-tert-butyl-phenol)) was incorporated in the reaction mixture.
U.S. Pat. No. 4,883,886, in discussing the addition reaction between viscous polyalkenes and anhydride reactants such as maleic anhydride, states that a known problem frequently encountered in this reaction is thermal decomposition and polymerization of the unsaturated anhydride reactant at temperatures above about 150.degree. C. According to the patentee, such thermal decomposition is accompanied by evolution of water vapor and oxides of carbon, and in a closed reaction vessel is accompanied by an increase in internal pressure. The patentee continues:
"Under some observed conditions, the thermal decomposition can be so rapid as to be explosive. In the absence of explosive thermal decomposition, a carbon-containing tarry residue is also formed in addition to water vapor and oxides of carbon. * * * Such thermal decomposition and attendant isomerization or polymerization of the unsaturated anhydride reactant has been observed as occurring during its addition reaction with polymeric olefins, e.g., polybutenes and others, in a closed reaction vessel. The carbon-containing residue varies in nature from somewhat granular when the decomposition is only slight to a tarry material mainly adhering to internal surfaces of the reaction vessel when the decomposition is more extensive but well below explosive magnitude. The granular type residue amounts to about from 0.1 to about 0.3 weight percent of the total charge and is generally dispersed in the alkenyl-substituted saturated anhydride addition compound product diluted with unreacted components of the olefin polymer, and is readily separated therefrom by filtration. However, the tarry residue product, which for the most part fouls the internals of the reaction vessel can be as high as 2-3 weight percent of the total charge. The tarry material not adhering to the internal surfaces of the reactor fouls the filter and interferes with filtration of the desired reaction product. Both types of residue are undesirable because of the above noted fouling characteristics and because their formation results in yield reduction of the desired alkenyl-substituted anhydride addition product."
The patentee refers to a number of other patents describing catalysts or agents which decrease such unwanted by-product formation, and utilizes such materials in a particular process in order to suppress the formation of tars and undesired side products.
U.S. Pat. No. 4,152,499 discloses that polybutenes having a higher proportion of terminal double bonds than conventional polybutenes can be produced by polymerizing isobutene with boron trifluoride as the initiator, if (a) the polymerization is carried out at -50.degree. C. to +30.degree. C., (b) from 1 to 20 mmoles of boron trifluoride are used per mole of isobutene, and (c) the mean polymerization time is confined to from 1 to 10 minutes. The patent further discloses that such polybutenes can be reacted with the stoichiometric amount of maleic anhydride, or a slight excess thereof, "in the conventional manner" at from 170.degree. C. to 250.degree. C., and that such polybutenes when heated with maleic anhydride for 4 hours at 200.degree. C. with stirring, followed by removing excess maleic anhydride under greatly reduced pressure exhibited a substantially greater activity than two commercial isobutene polymers. W. German Offenlegungsschrift 29 04 314 teaches the desirability of conducting the polymerization of the isobutene in the same manner except using a polymerization time limited to 1 to 40 seconds, and that to prepare mineral oil additives, "the polyisobutene is reacted in known fashion with the stoichiometric amount or a slight excess of maleic acid anhydride at 170.degree. to 250.degree. C."
It has also been disclosed heretofore that a specified thermal maleinisation reaction can be used to assess the quality (reactivity) of a polybutene polymer. In this procedure polybutene (50 g) is reacted with maleic anhydride (9.8 g), a 1:2 mole ratio, for 24 hours in a stirred reaction tube immersed in a bath of specified hydrocarbons under reflux at 210.degree. C. The reaction is conducted under nitrogen, and the reaction mixture is stirred at a specified number of revolutions per minute. A specifically designed apparatus is suggested for use in this procedure. The procedure results in the formation of both polybutenyl succinic anhydride and a complex resinous co-product formed from maleic anhydride.
As disclosed in our aforesaid prior application, Ser. No. 524,422, it has been found that substantial advantages can be realized by reacting an acidic reactant, such as maleic anhydride, with a substantially aliphatic polymer composed principally or entirely of polyisobutene in a mole ratio of acidic reactant(s): polymer is at least 1:1, provided that at least 50% (preferably at least 75%) of the polyisobutene content of such polymer has an end group represented by the formula ##STR2## and the reaction mixture is maintained under superatmospheric pressure during at least a substantial portion of the reaction period. Most preferably, the polymer consists essentially of polyisobutene (i.e., it contains at least 50 mole % and more preferably at least 60 mole % of polymerized isobutene) and at least 50% (more desirably at least 75%) of the total polymer(s) is polyisobutene having such end group.